Overall goals of our continuing program are to identify and develop anticancer clinical trial candidates, based on lead compounds that are isolated by using focused disease-oriented cytotoxicity, mechanistic, and molecular target based screening of selected medicinal plants, chosen either for their therapeutic use to treat cancer(s) or their structural novelty and potency. The fundamental aim of the proposed research is to discover novel anticancer drugs targeted primarily at key signal transduction pathways that regulate cell division, death, and differentiation. The following specific studies will be carried out to accomplish our goals. 1) Bioactivity-directed fractionation and isolation of the active principles from 30 high priority plant extracts will be continued. Our screening approach has been refined to stress molecular targets and several important signal transduction pathways and systems/elements of cellular differentiation and apoptosis. Two (2) important growth factor receptor tyrosine kinases (EGFR and HER-2) have been added as a new and complementary research initiative. 2) Structural characterization of new active leads will be done by chemical, physical, and spectral techniques. 3) Leads with significant activity will be selected for modification and analog synthesis to determine structure-activity relationships (SAR) as well as to improve pharmacological profiles. Conventional SAR, molecular modeling, and combinatorial chemistry techniques are used to aid lead generation and optimization. Compounds/plants of priority interest for investigation include breast cancer actives (e.g., neotanshinlactone and analogs, new active constituents of Quassia gabonensis), prostate cancer actives (new curcumin analogs), and differentiation/apoptosis inducers (new water-soluble dithiophene derivatives). 4) Subsequent in-depth mechanism of action studies and additional in vitro and in vivo antitumor evaluation will be performed by the National Institutes of Health (NIH) at the National Cancer Institute (NCI) as well as several corporate and academic collaborators. Our program has advantages of 1) an excellent supply of highly active lead compounds and promising cytotoxic plant species, including rainforest species from the NCI Natural Product Repository Program (NCI-NPRP), (2) excellent productivity in isolation and structural modification of new leads with new mechanisms of action as clinical trials candidates, which in turn could lead to innovative methods for cancer chemotherapy, and (3) a superior prospect for the successful development of a clinically useful drug, as several technologies have been licensed by corporate collaborators and are now undergoing further in vitro and in vivo preclinical and clinical assessment.